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During Leg 72 in the western South Atlantic, Cretaceous sediments were recovered only at Hole 516F (Rio Grande Rise). Late Cretaceous planktonic foraminifers were found in Cores 516F-89 through 516F-122 (between 964 and 1235 m sub-bottom); they are assigned to the late Coniacian to the latest Maestrichtian. Frequency and preservation of planktonic foraminifers are moderate in the upper Maestrichtian and deteriorate from there to the base. Only the upper Maestrichtian Abathomphalus mayaroensis Zone can be clearly delimited according to the generally accepted planktonic foraminiferal zonation; moreover, some of the more important zonal and stage boundary markers were not found. The Cretaceous/Tertiary boundary is well documented without any major hiatus, and in spite of the poorly recognized zonal boundaries, the Upper Cretaceous sequence is apparently continuous. There are possible correlations between planktonic foraminiferal distribution in Hole 516F and those in Site 356 (Sao Paulo Plateau) and Sites 357 and 21 (Rio Grande Rise). INTRODUCTION Hole 516F is situated near the crest of the Rio Grande Rise (western South Atlantic) in 1313 m of water depth (Fig. 1). At this site, a complete stratigraphic section of Upper Cretaceous through Recent sediments was recovered, terminating in basalt (Unit 8) of the SantonianConiacian at 1251 m sub-bottom. Cretaceous foraminifers occur within Lithologic Units 5B (part) and 6. Subunit 5B (between 930 to 1000 m subbottom) consists of reddish brown nannofossil limestones and contains the Cretaceous/Tertiary boundary in Core 516F-89 (964 m sub-bottom). Unit 6 is characterized by greenish grey and reddish brown limestones interbedded with marly limestones in Subunit 6A (10001130 m sub-bottom) and greenish grey to dark grey recrystallized dolomitic limestones in Subunit 6B (11301240 m sub-bottom). Both the reddish and the greenish intervals are bioturbated. The planktonic foraminiferal distribution at Hole 516F is comparable to those established in well-known sections of corresponding age (Sites 21, 356, 357) However, some of the more important Upper Cretaceous planktonic index markers (such as Globotruncana gansseri, G. calcarata, and G. elevatá) are not found. Therefore, the zonation based on planktonic foraminifers and the suggested age of the Upper Cretaceous deposits of Hole 516F discussed below is tentative except for the late Maestrichtian Abathomphalus mayaroensis Zone. The specific composition of planktonic foraminifers and other characteristics of the studied samples are listed on the distribution chart in the Appendix (backpocket); the distribution is shown in Figure 2. Unless otherwise indicated, all core numbers in the text refer to Hole 516F. Barker, P. F., Carlson, R. L., Johnson, D. A., et al., Init. Repts. DSDP, 72: Washington (U.S. Govt. Printing Office). BIOSTRATIGRAPHY Coniacian-Santonian Interval: Core 122 through Core 114, Section 5 The approximately 55 m of poorly lithified and recrystallized sediments (Core 125 through Core 119, Section 3) cannot be clearly delimited because of taxonomic difficulties. The lowermost microfaunal assemblage contains some very poorly preserved double-keeled planktonic foraminifers of the Globotruncana renzi-type, which were found in Section 516F-122-1. Within Core 119, the number of planktonic foraminifers distinctly increases. Globotruncanids (such as G. coronata, G. paraconcavata, G. fornicata, G. sinuosa, G. cf. undulata, G. cf. concavata, G. cf. pseudolinneiana, and Archaeoglobigerina cf. blowi) and heterohelicids (such as Heterohelix cf. reussi, H. globulosa, and Ventilabrella eggeri) occur in relatively low abundances; single-keeled globotruncanids were not found. No exact planktonic foraminiferal zonation or age assignment is given because these are mainly long-ranging planktonic species. The distribution of few specimens of Globotruncana cf. concavata (Core 119, Section 2, through Core 117) allows a possible subdivision of this interval. In Core 117, Section 1, the last occurrence of G. cf. concavata coincides with the first appearance of Ventilabrella eggeri; this horizon could be dated as middle to late Santonian. Campanian Interval: Sections 516F-114-4 through 516F-101-4 Well-known zonal markers of planktonic foraminifers are absent within this sequence. The Santonian/Campanian boundary discussed by Wonders (1980) was not clearly recognized at Hole 516F because neither Globotruncana elevata nor any true G. asymetrica ( = G. carinatá) could be identified. The boundary was placed, therefore, at the first appearance of G. area at Core 114, Section 4. According to various references (Pessagno,

Upper Cretaceous Planktonic Foraminiferal Biostratigraphy from the Rio Grande Rise: Site 516 of Leg 72, Deep Sea Drilling Project